The overall objective of this application is to improve electric field-forced gene transfer in solid tumors. Gene therapy has a great potential to improve treatment of different diseases, including solid tumors, but it has been impeded by the difficulties of gene delivery to specific cells. Recent reports by other investigators and ourselves have demonstrated that plasmid DNA delivery can be enhanced through the use of pulsed electric fields. However, present methods for optimizing electric field-forced gene transfer, in terms of electric pulse characteristics (e.g., field strength and pulse duration), are still empirical and incomplete. The fundamental hypothesis in this proposal is that electric field-forced DNA transport in the vicinity of cells determines the amount of gene transfer through the transient pores in the plasma membrane of cells created during in vivo electroporation. To test this hypothesis, we will systematically quantify the mechanisms of interstitial transport of DNA in response to different electric pulses both ex vivo (Aim 1) and in vivo (Aim 2). The quantification will be based on unique experimental methods developed in our labs, and it may result in an identification of effective pulse sequences for improving interstitial transport of DNA. The improved transport in the identified electric fields will be further increased through modifications in tumor tissue structures, using matrix enzymes, hypertonic solutions, or apoptotic agents (Aim 3). These chemical treatments transiently increase the interstitial space and thus decrease the resistance to DNA transport. Quantitative results from the transport studies in Specific Aims 1 through 3 will finally be used to improve transfection efficiency and therapeutic efficacy of interleukin- 12 gene in solid tumors transplanted in mice (Aim 4). The goal of the proposed study is to establish effective experimental protocols for improving interstitial transport of plasmid DNA which in turn may result in an increase in transfection efficiency in solid tumors without increasing toxicity.